"Block Control" is conventionally used to control train operation in most railway systems. In order to prevent collisions between trains running with a minimal distance therebetween, block control allows only one train to exist within a single block section of a railway line at a time, with a following train "blocked out" and prohibited from entering the block section. Security in train operation is thus attained by the block control system.
Known in common railway systems are two types of block control, one is a "fixed block" and the other is a "flexible block". In fixed block control, the automatic train control ATC is performed according only to the position of a preceding train. In flexible block control, the velocity of a subsequent train is also taken into consideration. In either of the block controls, the position of the preceding train is detected by a track circuit connected to the train and the railroads. A track circuit is provided for each block section which is predetermined according to a braking distance and an idle running distance of a subsequent train. In fixed block control, the borders of the block sections are fixed and cannot be changed. In flexible block control, wherein a block section may consist of a plurality of smaller sections integrally connected, the length of one block section can be varied by connecting or disconnecting the smaller sections to or from a block section, but the length of the smaller sections forming the block section are constant.
Additionally, a magnetic levitation railway system of on-ground primary propulsive type, hereinafter referred to as an on-ground linear railway system, requires another factor, in addition to the above mentioned factors such as braking distance, for performing the block control. The additional factor is the requirement that only a single train is allowed in a feeder section controlled by a substation. Therefore, in an on-ground linear railway system, the length of one block section for the purpose of performing the block control is determined as corresponding to one feeder section controlled by one substation.
Accordingly, in order to achieve shorter block sections while utilizing block control in the on-ground linear railway system, a substantial number of substations corresponding to each block section are required, reducing the cost-efficiency. As a result, the block sections for the on-ground linear railway system have been relatively long, and a reduction of cost-efficiency must be disregarded at stations where a number of railroad lines gather.
As a solution to this problem, a new method of controlling train operation was recently proposed whereby a plurality of sectional switching devices are provided on feeder lines to vary the feeder section length in an attempt to improve cost efficiency. Japanese Unexamined Patent Publication No. 4-185208 discloses such an apparatus which is utilized in performing the block control according to the newly proposed method.
Further, as a method for attaining an efficient on-ground linear railway system with existing substations, it was also proposed to change the feeder sections connected to each substation. For instance, only a single substation is provided for a plurality of feeder sections. Among the plurality of feeder sections, a feeder section having a train therein to be driven is designated from a control center and connected to the substation.
However, the alteration of the feeder sectioning and the switching of the connection between the substation and the feeder sections give rise to the following problems.
In an on-ground linear railway system, power is not supplied to all the feeder sections on a regular basis, in contrast to the contact wires of a common railway system. Instead, power is supplied only to the feeder section where power is required, and the acceleration and deceleration of a train is controlled by the amount of supplied power. Therefore, when there is no power supplied to the feeder section, the velocity of the train in the feeder section cannot be controlled. In other words, when a train enters a feeder section that is not controlled by a substation, the train can not be accelerated or decelerated. Thus, the method reveals a drawback in terms of security.
Further, the mentioned method of Japanese Unexamined Patent Publication No. 4-185208 neglects the need to look to the condition of a preceding or subsequent train in altering the feeder sections. As a result, when a feeder section is lengthened forward, a preceding train may be included in the same feeder section as the train in question, and the principle of "one train in one block section" is not maintained. If a feeder section is lengthened backward, the following train running behind the train in question may be included in the same feeder section, and will be suddenly halted.